The present invention relates to a method for making a semiconductor device.
Semiconductor devices include metal layers that are insulated from each other by dielectric layers. As device features shrink, reducing the distance between the metal layers, capacitance increases. To address this problem, insulating materials that have a relatively low dielectric constant are being used in place of silicon dioxide (and other materials that have a relatively high dielectric constant) to form the dielectric layer that separates the metal lines.
A material that may be used to form such a low k dielectric layer is carbon doped oxide. Using this material instead of silicon dioxide to separate metal lines may yield a device having reduced propagation delay, cross-talk noise and power dissipation. Although carbon doped oxide enables these favorable properties, films formed from that material may be relatively incompatible with conventional lithography processes. Such films"" optical reflectivity properties may prevent DUV (e.g., 157, 193, 248 nm) lithography from generating a sharp photoresist profile, which may cause CD control problems. This problem may be exacerbated if the carbon doped oxide chemically reacts with the photoresist.
Another issue relates to how conventional photoresist removal and post etch cleaning steps may affect a carbon doped oxide film""s dielectric properties. The carbon contained in such a film may react with materials used to remove the photoresist or to clean vias and trenches, depleting the amount of carbon contained in the film, which raises the dielectric constant. In addition, such films may crack or absorb moisture during these processes. Excessive moisture absorption can further degrade the film""s dielectric constant.
Accordingly, there is a need for an improved process for making a semiconductor device that includes a carbon doped oxide dielectric layer. There is a need for such a process that enables use of conventional lithography to form acceptable photoresist profiles. There is also a need for such a process that enables conventional photoresist removal and post etch cleaning steps to be used without significantly depleting the amount of carbon contained in the carbon doped oxide insulating layer. The method of the present invention provides such a process.
The present invention is a method of forming a semiconductor device having a carbon doped oxide insulating layer. That method comprises forming a first insulating layer that includes a carbon doped oxide. A second insulating layer is then formed on the surface of the first insulating layer. The second insulating layer has a surface that provides substantially uniform reflectivity, and protects the first insulating layer during photoresist removal and post etch cleaning steps.